The objective of this project will be to characterize in cytological and physical-chemical terms the chromosomes of dinoflagellates. Genetic recombination analyses of a variety of auxotrophic mutants of C. cohnii will be continued to detect linkage and crossing over. Mutagenesis experiments with Symbiodinium sp. will be done to attempt to recover thymine-requiring mutants. Renaturation kinetic and molecular weight measurements on several species of dinoflagellates will be completed in order to formulate a model for DNA sequence organization and structure in dinoflagellates. Studies on DNA replication will be initiated using several techniques (DNA/cell values as a function of cell cycle, microspectrofluorometric measurements on single cells and pulse label autoradiography) to determine where DNA replicates in the cell cycle and whether Y shaped chromosomes are actually replicating structures. Hybridization experiments will be performed to determine the relative similarity of the DNA's of various dinoflagellates species in an attempt to determine their taxonomic affinities.